The present invention relates to vertical takeoff and landing (VTOL) aircraft. More particularly, the invention relates to tilt wing VTOL aircraft.
There are design issues in known tilt wing VTOL aircraft. There is wing upper surface flow separation with the wing at mid-tilt angles during descending flight, when the propeller is at a reduced power setting and does not bend the air downward sufficiently before it reaches the wing to avoid wing upper surface flow separation. There is a major flow separation and associated buffeting area behind the wing segment over the fuselage at mid-to-high-tilt angles during climbing, level flight and descending transitions between cruise and hover flight, because there is no flow bending by the propeller in that area.
In the prior art, longitudinal pitch control in hover and at low transition speeds was provided by a horizontal variable pitch tail rotor driven by the main engines via shafting and a clutch, so that it may be disengaged in cruise flight. The known pitch control is thus complex and adds weight for equipment which serves no purpose except in hover and low speed flight.
In cruise flight, the propeller disc plane passes through the forward portion of the cabin, generally near the center of gravity. Design practice avoids the placement of passengers in this zone.
The principal object of the invention is to provide a tilt wing VTOL aircraft which functions efficiently, effectively and reliably throughout the speed range from hover to cruise flight at high power.
An object of the invention is to provide a tilt wing VTOL aircraft in which deflection of the wing tip area about a spanwise axis provides pitch control moments in hover and low speed flight.
Another object of the invention is to provide a tilt wing VTOL aircraft having a considerably diminished spanwise wing lift distribution near the center and hence more tolerance to high angles of a attack when the wing is in a position for speeds well below the conventional airplane stall speed, but not in a full hover.
Still another object of the invention is to provide a tilt wing VTOL aircraft which permits low propeller power settings and thus more desirable low speed performance during descent, when the wing is in mid-tilt positions.
Yet another object of the invention is to provide a tilt wing VTOL aircraft having reduced intensity of center section buffet.
An object of the invention is to provide a tilt wing VTOL aircraft having simple pitch control, yaw control and roll control throughout the speed range from hover to cruise flight.
Another object of the invention is to provide a tilt wing VTOL aircraft having an increased fuselage volume near the center of gravity not subject to the hazard of the propeller disc plane.